/Engine/Source/Runtime/Engine/Public/Rendering/SkeletalMeshVertexBuffer.h
Base vertex data for GPU skinned skeletal meshes make sure to update GpuSkinCacheCommon.usf if the member sizes/order change!
struct TGPUSkinVertexBase
FPackedNormal
TangentX
Tangent, U-direction.
FPackedNormal
TangentZ
Normal.